1. Field of the Invention
The present invention is directed to a thermoelectric semiconductor compound and a method of making the thermoelectric semiconductor compound.
2. Description of Related Art
It is well known that thermoelectric semiconductor compounds exhibit the Seebeck effect, where heat is converted to electricity, and the Peltier effect, where application of an electric current causes cooling or heating.
The thermoelectric performance of a thermelectric semiconductor compound is indicated by a performance index Z (=.alpha..sup.2.sigma./.kappa., where .alpha. is the Seebeck coefficient, .sigma. is the electrical conductivity, and .kappa. is the thermal conductivity). A higher performance index Z results in higher thermoelectric performance. For example, a higher performance index Z results in a higher voltage being developed if a temperature difference is provided across a thermoelectric semiconductor. A higher performance index Z also results in a larger temperature difference being developed across a thermoelectric semiconductor upon application of an electric current. Thus, much research and development effort has focused on increasing the performance index Z to as high a value as possible.
One improved thermoelectric semiconductor compound is disclosed in Japanese Laid-open Patent No. Hei. 10-242535, which was published, without examination, on Sep. 11, 1998. The performance index Z was increased by adding BN to a thermoelectric semiconductor with a molecular formula of (Bi.sub.2 Te.sub.3).sub.70 (Sb.sub.2 Se.sub.3).sub.5 or (Bi.sub.2 Te.sub.3).sub.70 (Sb.sub.2 Se.sub.3).sub.30, even though the addition of BN led to a reduction in thermal conductivity.
Another improved thermoelectric semiconductor compound is disclosed in Proc. XII Int. Conf. On Thermoelectric, IEEJ, Tokyo, Yokohama (Japan), pp.121-125, 1994. The performance index Z was increased by a factor of 1.2 by the addition of 2 volume % MgO, in the form of powders having an average diameter of 0.01 .mu.m, to a thermoelectric semiconductor having a molecular formula of (Bi.sub.0.25 Sb.sub.0.75).sub.2 Te.sub.3.
In both cases, the performance index Z of a thermoelectric semiconductor compound was increased by the addition of a dielectric material that also decreased the electrical conductivity. Thus, the increases in the performance index Z resulted from an improvement in one or more of .alpha. and 1/.kappa., while .sigma. was sacrificed. As long as improvements in the performance index Z require a trade-off of one or more of the factors of Z, improvements in Z will be limited.
Accordingly, a need exists for a thermoelectric semiconductor compound with a remarkably improved performance index Z that is not the result of sacrificing one of the factors of Z.